The present invention is a method for guiding a thin web material to form or fold the thin web material. The unformed web material is conveyed over a first and second guide roll. The shape of the web material is then formed over a triangular former and forming rolls.
The present invention also relates to an apparatus for guiding and forming the thin web material. The apparatus includes a first and second guide roll, a triangular former and two forming rolls.
It is a generally known principle that in forming a thin web material, such as a plastic material, the web material is conveyed over a triangular former. This method is, for example, used to make bags and similar products when it is desirable to fold a single web material. The method may briefly be described as passing the web material over a baseline side edge of the triangular former and then folding the web material when the web material reaches the opposite corresponding tip of the triangle. The folder web material is thereafter usually guided between forming rolls that convey the web material forward for further processing.
The unfolded web material may be unevenly wound on a supply roll, unevenly cut or unevenly conveyed through the apparatus. This results in the edges of the web material not being exactly aligned when the web material is folded. Depending on the application, this deficiency may be adjusted for by using a wide joint where the edges are sealed together or the protruding sealed edges may be cut from the folded web material. This method is used when bags are manufactured. For other applications, such as folding of textiles, it does not matter whether the edges are exactly aligned.
To be able to exactly align the edges when web material is folded, some sort of guidance of the web material is required to adjust for the problems mentioned above. The edges must be aligned with high precision when, for example, package materials are made where the sealed joint is located at the outside of the package. To make the package material aesthetically appealing, it is desirable to align the edges with as high a precision as possible. Another advantage of guiding the edges so that they are perfectly aligned is that the material cost is reduced and a much more narrow joint may be used where the edges are sealed.
An object of the present invention is to provide a method and an apparatus to guide a thin web material to adjust for: misaligned conveyance of the web material through the apparatus, uneven winding of the web material or unevenly cut web material.
A further object of the present invention is to provide a method and apparatus for guiding a web material so that the difference between the length of the generatrices of the side edges and the center line of the web material is very small.
A further object of the present invention is to provide a method for folding a thin web material so that machine costs may be reduced because the requirements of precise guidance of the web material through the machine are reduced.
These and other objects are achieved by the method of the present invention because the triangular former, whose baseline is secured to the second guide roll, may be tilted back and forth about a longitudinal axis of a bearing axle extending through the tip of the triangular former that is opposite the baseline of the former. The longitudinal axis is parallel to the web material when the web material is conveyed between the first and the second guide roll. The tilting of the triangular former is dependent upon a noncontacting scanning device that scans at least one of the edges of the web material.
These and other objects have also been achieved by the apparatus of the present invention because the baseline of the triangular former is secured to the second guide roll and the triangular former and the second guide roll are movably attached to the apparatus so that they may be tilted relative to the longitudinal axis that extends through the tip of the triangle so that this longitudinal axis is parallel with the web material when the web material is conveyed between the first and second guide roll. The apparatus also includes a member that is secured to the second guide roll for non-contacting scanning of the edges of the web material. The member is arranged to control the position of the triangular former and the second guide roll.
The preferred embodiments of the present invention are further described in the claims.